As a material for food packaging, plastic having improved heat resistance and the like is now being used increasingly. And, polyethylene-2,6-naphthalate (PEN), which is one type of polyester resin, is particularly superior to polyethylene terephthalate (PET) in mechanical strength (Young's modulus, breaking strength), heat resistance (long-term heat stability, dimensional stability), ultraviolet shielding property (weather resistance), chemical properties (chemical resistance, gas barrier properties) and the like because of inflexibility and planarity of its molecular chain, and has come into the limelight in recent years. But, it has inferior heat-sealing properties with a lid material. Specifically, it has poor heat-sealing properties with an aluminum closure (aluminum foil lid material) which has a polyester based adhesive layer as the innermost layer and also inferior adhesive force depending on use conditions. And, because the forming conditions are different when the PEN resin is contained, it cannot be included in a recycling system of the PET resin and also has the same drawback as the multi-layered film view of recycling efficiency. Besides, there were also problems of impact resistance and high cost.
The present inventors have proposed, as packing materials for food which are free from the drawbacks of polyethylene-2,6-naphthalate (PEN), a polyester copolymer indicated by a general formula, HO—(COArCOORO)n—H (n is 100 to 1000. But, Ar is 2,6-naphthalene group and phenylene group, and R is ethylene group and 1,4-cyclohexylene group.) (Japanese Patent Application Laid-Open Publication No. Hei 8-113631) and a laminated sheet made of a polymer alloy formed of a polyarylate resin and a thermoplastic polyester resin (Japanese Patent Application Laid-Open Publication No. Hei 11-34271).
The former copolymer excels in heat resistance, impact resistance, heat-sealing properties with a lid material, gas barrier properties and recycling efficiency, but the copolymer has a problem of high cost when it is used as a single-layer film for a food packaging container. And, the latter laminated sheet is superior in heat resistance, impact resistance and heat-sealing properties with a lid material but insufficient in gas barrier properties, flavor resistance (flavor attack resistance) and aroma retention. For example, when it is used as a jelly container, it has a problem of being limited by used flavor.
It is an object of the present invention to remedy the problems of the prior art and to provide a transparent plastic laminated sheet which has sufficient flavor resistance and aroma retention and also excels in gas barrier properties (oxygen barrier properties), impact resistance, heat resistance, sealing properties and cost efficiency.
And, its object is to provide a transparent plastic laminated sheet which excels in heat-sealing properties with a lid material and recycling efficiency, has sufficient flavor resistance and aroma retention, and also excels in gas barrier properties (oxygen barrier properties), impact resistance, heat resistance, cold-impact resistance and cost efficiency.
Besides, its object is to provide a packaging container for food, drink and the like, which is formed of the above-described plastic laminated sheet.